Irrigation Efficiencies and Lint Yields of Upland Cotton Grown at the
Maricopa Agricultural Center, 1997
Mike Sheedy, Maricopa Agricultural Center
Jack Watson, Maricopa Agricultural Center
A field trial was conducted at the Maricopa Agricultural Center to observe
the effects of four irrigation efficiencies (65%, 75%, 85%, and 95%) on the
lint yield produced from two upland cotton varieties (DP 5409 and SG 125).
Nitrogen requirements for the crop were determined using pre-season soil samples
and in- season petiole samples in conjunction with crop monitoring data collected
at weekly intervals. AZSCHED was used as a guide to the irrigation timing and
amount of water applied during the season. This year there was a lint yield
response to the different irrigation efficiencies, and a slight difference in
yield between the two varieties. Lint yields were significantly lower in the
95 % irrigation efficiency plots. Lint Yields ranged from 1448 # lint/acre
( SG125 at 75 %) to 1220 # lint/acre ( DP5409 at the 65 % irrigation
Water management and conservation can significantly reduce costs associated
with cotton production. Improving irrigation efficiency on any particular field
can conserve a large amount of water over the growing season. An efficient
irrigation system will provide enough water to meet the growing requirements of
the crop without any yield loss due to water stress while also providing enough
extra water to leach salts past the root zone.
Increasing the efficiency of irrigations can be a costly and difficult
endeavor. In 1991, at the Maricopa Agricultural Center (MAC), the first
(pre-)irrigation required up to 10 acre-inches/acre of water to completely wet
the seedbed (Sheedy and Watson 1992). In that particular field the soil water
holding capacity is 1.6" per foot, so the pre-irrigation water actually saturated
the soil profile to a depth of 6'. Residual water present in the soil profile
before the pre- irrigation is replaced and becomes unavailable for crop use.
The practical root zone of the cotton crop until the first post emergence
irrigation is about 2' deep, so the water that saturated the soil from 2' to 6'
deep can be considered excess application of over 6". This excess results in
less than 50 % irrigation efficiency.
Reducing the amount of water applied at the first irrigation of the season
would save money and reduce the potential for loss of fertilizer salts due to
leaching. An increased irrigation efficiency is often the result of an
improvement in irrigation application uniformity. We have employed different
methods in recent years in attempts to improve the uniformity and efficiency
of the first irrigation. In 1990, a tractor was driven up and down the furrows
to compact the soil and allow the water to run the length of the field unimpeded
by large dirt clods present in the furrows (Scherer et. al. 1991). An increased
water flow at the head end of the field was used to improve irrigation efficiency
in 1992 (Sheedy and Watson 1993). The use of torpedoes can improve uniformity and
thus reduce the amount of water required in an irrigation (Schwankl et. al. 1992). Short runs also allow a more uniform distribution of water across the field. These approaches, of course, applies to a laser leveled field in a basin irrigation setting.
Crop monitoring and plant growth characteristics can be used as a tool to
follow the nutrient requirements and the overall health of the crop. Guidelines
for different crop characteristics have been available from previous cotton
reports (Silvertooth et. al. 1993). These guidelines are independent of the
cotton variety grown and provide baselines and thresholds for the expected growth
and development of cotton. The observations of Height:Node (H:N) ratios and
petiole nitrate analysis are useful in the timing of fertilizer applications.
As the season progresses, the nodes above white bloom (NAWB) and the fruit
retention are recorded. The number of NAWB's indicate cutout and help in deciding
the terminal irrigation (Silvertooth 1994). Regular monitoring of the crop
would signal a trend in the crop growth and alert the grower to needed management
decisions as well as provide the basis for these decisions.
In 1997, two upland cotton varieties were grown in a field at MAC. These two
varieties were irrigated at four irrigation efficiencies to observe the effect of
differing amounts of applied water on the crop growth characteristics and lint
Materials and Methods
A split plot design was used to compare lint yields from DP 5409 and SG 125
grown at four irrigation efficiencies (65%,75%,85% and 95%). For each
efficiency, there was a different amount of water applied to the crop at
irrigation time. Lower efficiencies, of course had a greater amount of water
applied than the higher efficiency treatments. Timing and amount of irrigation
was determined by using the computer model AZSCHED.
The previous crop on this field was a pasture of barley used for grazing
sheep. Pre-season soil samples showed a need for additional nitrogen fertilizer.
On February 4, nitrogen was applied as ammonium sulfate (21-0-0) at a rate of
40 #N/acre. Field preparations were completed on March 17 1997. Before
pre-irrigation, a tractor was used to compact each furrow bottom. On March
20, the field was pre-irrigated with an average of 6 acre- inches of water and
on April 7, the upland cotton varieties were planted at a rate of 8-10 #
Each plot was 400' long and six (40") beds wide. Ten additional irrigations
were scheduled during the growing season up to August 8th. The following
irrigations were based on the AZSCHED computer program. In the past AZSCHED
has called for irrigations when the soil depletion of available water was
actually greater than 50%. This is an indication of crop stress. To remedy
any crop stress, in 1991 the irrigation was performed at least one day
before the day AZSCHED had scheduled. It was hoped that any crop stress
could be avoided in this manner. Water was measured and applied by the use
of an in-line meter and gated poly-pipes.
Ammonium sulfate was side dressed to the crop at a rate of 45# N/a on May 6
and June 11. Defoliant was applied on September 3 and the crop was harvested on
September 22. The two middle rows of each plot were harvested for yield.
Subsamples of seed cotton from each plot were taken to determine lint yield
and gin turnout.
Observations of plant growth characteristics were taken on a weekly basis to
monitor the growth and development of the cotton crop. Petiole samples were
analyzed for nitrates at MAC with use of an ion selective electrode. Height
to node ratios and fruit retention levels were also recorded at the same time.
Results and Discussion
Results and data of the yield trial are presented in
Table 1 and
Figure 4, and Figure 5.
Lint Yield and Irrigation Efficiencies
There was a difference in lint yield and seed cotton yield due to
the irrigation efficiencies, and a slight difference in lint production
between the two cotton varieties DP 5409 and SG 125. The least amount of
seed cotton and lint produced was from DP 5409 at the 65% irrigation efficiency
which produced 3484 # seed cotton and 1202 # lint /acre. The largest amount
of lint produced was from SG 125 (1448 # lint and 4138 # seed cotton /acre)
when irrigated at a 75 % irrigation efficiency. Actual irrigation efficiencies,
ranged from 60 % to 75 %. The inherent inefficiency of early season irrigation
is the main cause for lower the than targeted irrigation efficiencies of 65 % to
Crop Monitoring (Figure 1,
Figure 2, and
Cotton petioles were collected at weekly intervals for preparation of
nitrate analysis. Height to node ratios and fruit retention levels were
obtained at the same time. Fertilizer applications were timed in accordance
with petiole nitrate levels and height to node ratios
and Figure 3). Height to node ratios as
well as fruit retention levels remained well within the upper and lower
thresholds during the season, so there were no great shifts between vegetative
or stressed growth. Petiole nitrate levels remained within the adequate range but
dropped below this level towards the end of the season. Overall, the results of
this year's crop monitoring showed a healthy crop with little or no stress
recorded and yields greater than in previous years.
- Scherer, T., Slack, D, Watson, J., Fox, F. 1991. Comparison of Three Irrigation Scheduling Methods and Evaluation of Irrigation Leaching Characteristics. Cotton: A College of Agriculture Report. Series P-87, 100-102.
- Schwankl L.J., Hanson B.R., Panoras, A. 1992. Furrow Torpedoes Improve Irrigation Water Advance. California Agriculture, November-December 15-17.
- Sheedy, M. and Watson, J. 1993. Irrigation Efficiencies, Nitrogen and Phosphorous Applications, and Lint Yields of Upland Cotton Grown at the Maricopa Agricultural Center, 1992. Cotton: A College of Agriculture Report. Series P- 94, 312-315.
- Sheedy, M. and Watson, J. 1992. Irrigation Efficiencies, Nitrogen Applications, and Lint Yields of Upland Cotton Grown at the Maricopa agricultural Center, 1991.
- Silvertooth, J., Brown, P.W., Malcuit, J.E. 1993. The Development and Delivery of a Crop Monitoring Program for Upland and Pima Cotton in Arizona. Cotton: A College of Agriculture Report. Series P-94, 17-26.
- Silvertooth, J. 1994. Practical Uses of Crop Monitoring for Arizona Cotton. Cotton: A College of Agriculture Report. Series P-96, 18-23.
- Sheedy, M. and Watson, J. 1994. Irrigation Efficiencies and Lint Yields of Upland Cotton Grown at the Maricopa Agricultural Center, 1993. Cotton: A College of Agriculture Report. Series P-96, 224-228.
This is a part of publication AZ1006:
"Cotton: A College of Agriculture Report," 1998, College of Agriculture,
The University of Arizona, Tucson, Arizona,
85721. Any products, services, or organizations that are mentioned, shown, or indirectly
implied in this publication do not imply endorsement by The University of Arizona.
The University is an Equal Opportunity/Affirmative Action Employer.
This document located at http://ag.arizona.edu/pubs/crops/az1006/az10065b.html
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